Protective system for power-plant installations



1,641,691 R. POHL PROTECTIVE SYTEM FOR POWER PLANT INSTALLATIONS Filed Sept. 22 1924 In\/ ent or Robert Pohl, by M 14? H is Attorney Patented Sept 6, 1927.

UNITED STATES TATENT QFT EQE,

ROBERT POHL, OF BERLIN, GERMANY, ASSIGNOB T GENERAL ELECTRIC COMPANY, A COREORATION OF NEW? YORK.

PROTECTIVE SYSTEM FOR POWER-PLANT INSTALLATIONS.

Application filed September 22, 1824,Seria1 No. 739,004, and in Germany November 27, 1923.

The present invention relates to protective systems for power plant installations comprising electrical generators driven by prime movers, and has for its object the provision of an improved arrangement in aprotective system of the above-named type whereby in the event of overload or similar electrical disturbance on the line-or source of load to which a generator is connected, the generator may be automatically and safely disconnected therefrom without affecting the operation of its prime mover, and in the event of internal short circuit or similar electrical disturbance more directly associated with the generator, its prime mover may be in addition automatically cut off from its supply of motive fluid and brought to rest.

A protective system embodying the invention is herein described, by way of example, in connection with a power plant installation comprising an alternating current generator directly connected to a steam turbine of the condensing type. This is diagrammatically illustrated in the accompanying drawing, to which fora more complete understanding of the invention, attention is new directed.

Referring to the drawing, 3 is a steam turbine having a high pressure steam inlet conduit 4- controlled by a quicleclosing emergency valve 5, and an exhaust conduit 6 connected with a surface condenser 7. The exhaust conduit is provided with a normally closed atmospheric inlet valve 8 which, when opened, breaks the vacuum on the condenser and subjects the interior of the turbine and condenser to atmospheric pressure.

The valve 8 is held in the closed position against the action of a spring 9 tending to open it, by a latch member 10. At one end the latch member releasably engages the valve stem indicated at 11, which at the opposite end is pivotally mounted in a fixed supporting bracket 12. Adjacent the latch member is an electromagnet 13 which when energized attracts it in a direction to cause it to disengage the valve stem and permit the valve 8 to open under the action of spring 9. The valve arrangement shown represents any suitable arrangement providing a valve which will automatically open whenreleased and which is capable of being electrically tripped. I

The emergency valve is similarly controlled by an electromagnet 14, except that in this case the valve is normally held in the open position against the action of a spring 15 tending to close it. A latch member 16, holds the valve in said open position by engaging with the valve stem indicated at 17, and is pivotally mounted in a fixed support bracket 18 in such a manner that it will move in the direction of the electromagnet when the latter is energized, thereby releas ing thevalve stem 17 and permitting the emergency valve to close. The emergency valve may be of any suitable type which is self-closing and which is capable of being electrically tripped. The turbine may be provided with the usual throttle valve in advance of the emergency valve. However, as the throttle valve forms no part of the invention, it has been omitted for the purpose of simplifying the drawing and description.

Directly connected with the turbine by a shaft 19 is an alternating current generator indicated in outline by the dotted lines 20. Within the generator are provided alternating current windings 21, 22 and 23, and a direct current field winding or exciting field '24. The generator represents the usual revolving field type and is for this rea P videdwith slip rings 25 to which the field 24 is connected. The alternating current windings are by way of example, provided for three phase operation and are Y-connected to a common neutral lead 26 which is grounded as indicated at 27 through a suitable resistor 28. The output ends of the alternating current windings are connected ill) to three-phase terminals 29 from which the output of the generator is conducted by a three-phase lead or cable 30 to. a three phase line switch indicated at 31. Theline switch is indicated as being in the closed position engages with theend of a plunger-36 of asolenoid magnet 37 and is released by the withdrawal of the plunger when the solewan noid is energized. The line switch epresents any suitable circuit interrupting device which automatically operates to disconnect the generator from'the line when actuated by a trip device such as the solenoid 37.

Excitation for the field winding 24 of the generator is supplied by a shunt-wound direct-currentgenerator or excite]: 38. This exciter is connected with the generator slip rings by leads in one of which loads is d a field rheostat 4:0 for controlling nt in the held 24. in circuit with esistor -13, the latter being shunted by a w tch which is normally closed. The

pu )ose of this resistor is to reduce the exitation of the alter ating current generator 20 by lo.vermg the voltage of the exclter and hence the current in the field 2e when the switch is opened. The use of this re-- sister will more fully appear hereinafter under the description of the operationjof the system.

The switch e l is held in the-closed position by an. arrangement similar to that provided for the line switchill. "llhi comprises a catch member carried by the switch, a solenoid magnet L6 having: a plunger 47 which engages with the catcluand a spring elf? which opens the switch when the solenoid is energized and the plunger is withdrawn from engagement wvith the catch member.

In circuit with the generator phase windin s 21, 22 and 23 are the piunary windings of two sets of current transformers, one set lteins placed between the generator windings e neutral lead 26 as indicated at 9 other setbeing; placed between the and the line s vitch 31 as indicated Thus there are two transformers in "use, one in the neutral leg); adjacent i ral lead 26, and one in the output adjacent the line switch 31. Tiie secondary windings of the two transformers in phase2l are shown at 51 and 52.

I These are connected together by a series circult 53, so that in operation a circulating current flows through them. As this represents a well known arrangg'en'icnt and consecondaries 51 and By this arrangement the actuating coil 57 of relay 58 is subjected to the circulating current which flows through the secondaries 51 and52 when load current flows through their respective primary windings, and is arranged to cause a pair of normally open contacts 59 and 60 to close when this circulating current reaches a predetermined high value, corresponding for example to an overload on the line 32, while the actuating coil 55 of relay 56 is energized only when a differential current flows thr ughit from the secondaries 51. and 52 as a result of a condition of operation setting up a difference between the current flowing through the generator winding 21 and the line connected with it. Such a condition of operation is represented, for example, by an internal short circuit or ground at some point within the generator or cable 30, that is between the current transformers 4:9 and 50, accompanyin a breakdown of the insula- Lion when a greater current will flow through the primary associated with the secondary 51 than will flow through the primary associated with the secondary 52. The coil 55 arranged to close a pair of normally open contacts 61 and 62 when the differential current reaches a predetermined low value.

7 In brief the arrangement above described is such that relay 58 operates when an exter nal electrical disturbance develops at any point beyond the current trans-former 50 in the direction of the line 82, such as a pre determined overload, ground or short circuit on said line while relay 56 operates when an internal electrical disturbance occurs. The term internal electrical disturbance as used herein is intended to include any disturbance in the nature of a ground or short circuit which may develop in the generator windings, its connecting cable 30, or either sctof t nsformers l9 andv 50, and is used to distinguish such disturbances from external electrical disturbances mentioned above. The secondaries and connections for the transformers in phases and 23 of the generator, which have been omitted for reahereinbefore pointed out may be considerered to be the same as shown in connection with 21' and to be provided with overload and different ally operated relays.

lravingcontacts which are connected in parallel with those of relays '58 and 56 respectively.

The electromagnets 13 and 14 and the solenoid magnets 37 and 46 are energized from supply mains indicated-at 63 and 6% through circuits controlled by the contacts of the relays 56 and 58. The supply mains 63 and 64L should preferably be maintained at a constant voltage and should provice substan- This may be accomphshed by connecting them with a Ian source of constant potential energy, such as for example, a storage battery (not shown).

Electromagnets 13 and 14 connected in parallel to a circuit 65, one side of which is connected to the upper contact 61 of relay 56 and the other side of which is connected to one side 63 of the supply mains 63, 6s. The solenoid magnets 37 and 16 are connected in parallel to a similar circuit 66, one side of which is connected to the lower contact 62 of relay 56 and to the upper contact 59 of relay 53, while the other side is connected to supply main 6%. The remaining contact 60 oi relay 53 is connected by a lead 67 to the supply main 63.

The above arrangement is such that when the contacts 59 and 60 of relay 58 are closed, a circuit is closed from supply main 63 through the lead 67 and contacts 60 and 59, through solenoids 3'7 and 4:6 in parallel by way of one side oi"- circuit 66, and back through the opposite side of circuit 66 to the supply main 6%, thus causing the solenoids 3'? and 6 to be energized by placing them in parallel across the supply mains 63 and 64. lVhen the contacts 61 and 62 of relay 56 are closed, a circuit is closed from the supply main 63 through one side of circult through both electromagnets 13 and 1 1 in parallel, back through the opposite side of circuit 65, through the contacts 61 and 62 to one side 01 circuit 66, through both soleitids 3''? and $6 in parallel 'andback through the opposite side oi circuit 66 to the supply main 6%, thus causing the solenoids 3? and d6 and electromagnets 13 and 14 to be energized by placing the parallel-ed solenoids in with the paralleled electromagnets across the supply mains 63 and 6 1 The solei'ioids and electromagnets are designed so that the reduction in current caused by plac in? them in the above series relation does not a. set their proper operatioin The operation 01" the system is as follows: lVith the generator in operation and delivering power to line 32, min switch 31 is closed, the eXciter field resistor 43 is short circuited by the closed switch l emergency valve is open and atmospheric relief 8 is closed, said switches and valves being latched in their respective operating positions, all as indicated in the drawing.

'Vl hen overload on the line 32 or similar external electrical disturbance develops, the relay 58 is operated to close contacts 59 and by a corresponding overload current flowing through the secondarie: 51 and The solenoids and 46 are then energized and the main switch 31 and switch are tripped open. As the overload is thus suddenly taken off the generator by the opening of the main switch 31, thevoltage delivered by itmay rise to a high value, that is, to a value sufficiently high to dangerously stress the insulation. This condition is prevented in the arrangement shown by the simultaneous opening of theswitch a l, which, as hereinbetore explained, reduces its excitation and consequently el'lects a lowering of its output voltage.

The normal operation is restored by reclosing switch as after adjusting the exciter field rheostat e2 so that this will not raise the generator output voltage above a permissiblehigh value and then reclosing the main switch 31 alter finally adjusting the generator output voltage to the. proper value by either the exciter iield rheostat 4:2 or the generator field rheost: t i0.

It internal electrical disturbances develop, that is, disturbances in the nature of a short circuit or ground at any point between trans iormers andhO, or even within transformers 50, the resulting ground or short circuit current flow will not pass through transformers 50, but only through transformers 19; hence an unbalance between the utput of secondaries 51 and 52 will be set up and the relay 56 will operate to close contacts 61 and 62, thus energizing the magnets '13 and 14; as well as the solenoids 37 and d6. This eiiects the opening of switches 31 and 4 1 as before explained and in addition it etitects the tripping of the valves 5 and 8, emergency valve 5 closing and atmospheric inlet valve 8 opening. Thus upon the deveTopment of. internalelectrical disturbances sutlicient to operate relay 56, the generator is cut ofi from the line and its voltage reduced by the opening of switches 31 and it as in the case of external electrical disturb ances. in addition the turbine is cut-oft LlI'OlH its supply by the closing of emergency valve 5 whereby it will come to rest, and atmospheric pressure is admitted to the in terior' ot the turbine and condenser by the opening of atmospheric inlet. valve 3, whereby a braking load will be applied to the moving parts of the turbine through increased windage resistance, to bring the turbine to rest more rapidly. V v

The protective system provided, thus opei ates to cut off the generator from the line upon the occurrence ofeither an internal or an external electrical disturbance. Since the external disturbances are ordinarily temporary in nature, the system provides that the turbineor prime mover is kept in operation during their occurrence but in the case of internal disturbances which are usually accompanied by damage requiring attention and repairs, the system further provides for stopping the prime mover, the stopping preferably being hastenec by admitting atmospheric pressure to'the interior of the prime mover. V

The lowering ot the generator excitation is, especially desirable under internal short circuit conditions as it serves to lower the short circuitcurrent which may be set up thereby, and, in case the internal electrical disturbance results in fire within the generator, the rapid stopping ot-the generator is especially desirable, this being provided in the present example, by the admission of atmospheric pressure to the prime mover, as above mentioned.

The ground resistor 28 is provided in the neutral, grounded lead 26 to limit to a certain low value the current which may flow as a result of a grounded phase, either external or internal. The resistor is, however, such that suliicient current will be passed by it to cause the relay 58 to operate it the ground is in the nature of an overload on the line, and to cause relay 56 to operate it the ground is internal, that is, within the cable 30, the generator windings or the current transformers i9 and 50.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I consider to rep resent the best embodiment thereof, but I desire to have it understood that the apparatus shown isonly illustrative, and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

The combination with a prime mover an electrical generator connected therethe generator from said circuit, means responsive to external electrical disturbances for operating saiddisconnecting means, and means responsive to internal elec trical disturbances for operating said disconnecting means and stopping the prime mover, said second and third named means including in common a current transformer connected with the generator, and a current transformer connected between the generator and the external circuit, said transformers having secondaries connected to form a series circuit, said second-named means including a current-responsive device in said series circuit, and said third-named means including a current-responsive device connected across normally neutral points of said series circuit.

2. The combination with a prime mover having a motive fluid supply and an electrical generator connected with the primemover, of an external electrical circuit connected with thegenerator, means for disconnecting the generator from said circuit, means responsive to external electrical disturbances for operating said disconnecting means, and means responsive to internal electrical disturbances for operating said disconnecting means, cutting off the motive fluid supply from the prime mover and applying abraking load to stop said prime mover and connected generator, said means including in common a current transformer connected with the generator, and a current transformer connected between the generator and the external circuit, said transformers having secondaries connected to form a series circuit, said first-named means including a current-responsive device in said series cir cuit, and said second-named means including a current-responsive device connected across normally neutral points of said series circuit.

3. The combination with a prime mover and an electrical generator connected therewith having an exciting field, of a source of electrical load connected with the generator, a switch in said connection, means responsive to overload on the generator for simultaneously opening said switch and reducing the excitation of the generator field, and means responsive to internal electrical disturbances associated with the generator for simultaneously opening the switch, reducing the excitation of the generator field and stopping the prime mover, said means having in common a control circuit connected with the generator and a controlled circuit, a portion otwhich last-named circuit is controlled by said first-namel means and all of which last-named circuit is controlled by said second-named means.

4;. In combination, an elastic fluid prime mover having an elastic fluid inlet and an emergency rapid-closing valve controlling said inlet, an electrical generator connected with said prime mover, an exciting field for the generator, a source of load to which the generator is connected, a switch in said connection, relay-controlled means responsive overload on the generator for simultaneously opening said switch and reducing the excitation of the generator field, and relay controlled means responsive to internal electrical disturbances associated with the gen erator for simultaneously opening said switch, reducing the excitation of the generator field and permitting the emergency valve to close, said means having in common a control circuit connected with the generator and a controlled circuit, a portion of which last-named circuit is controlled by said first-named means and all of which last-named circuit is controlled by said second-named means.

5. In combination, an elastic fluid prime mover having an elastic fluid inlet and an exhaust outlet, a condenser connected with said exhaust outlet, a normally closed atmospheric inlet valve for the prime mover adjacent the exhaust outlet, said valve being releasable to automatically open, a normally open emergency rapid-closing valve controlling the elastic fiuid inlet, said valve being releasable to automatically close, an electrical generator connected with the prime mover, an exciting field for the generator, a source of load to which the generator is connected, aswitch in said connection, relaycontrolled means responsive to overload on the generator for simultaneously opening said switch and reducing the excitation of the generator field, and relay-controlled means responsive to internal electrical disturbances associated with the generator for simultaneously opening the switch, reducing the excitation of the generator field and releasing the emergency and atmospheric inlet valves, said means having in common a control circuit connected with the generator and a controlled circuit, aportion of which last-named circuit is controlled by said firstnamed means and all of which circuit is controlled by said second-named means.

6. The combination with a prime mover and an electrical generator connected therewith having an alternating current winding, 01": an external electrical circuit connected with said winding, a switch in said connection, current transformers in circuit with the generator winding on each side thereof, said transformers having secondaries connected to form a series circuit, a relay hav ing an operating coil connected in said series circuit, a second relay having an op erating coil connected with normally neutral points in said series circuit, means controlled by said relays for disconnecting the generator winding from the external circuit, and means controlled by the second-named relay for stopping the prime mover.

In witness whereof, I have hereunto set my hand this 27 day of August, 1924:-

ROBERT POI-IL. 

